Intelligence of computers is largely dependent on the sophistication of their external memory. At present, the overall speed of computers is lower by two or three orders than that of their computing units precisely because of inadequate external memories. Basic technical characteristics of external memories include information capacity, recording density, access time, information exchange speed, and storage reliability. Optical external memories possess certain advantages as contrasted to magnetic external memories, such as larger capacity, greater density and reliability and are therefore more promising.
Known in the art is an optical memory (IEEE Spectrum, 1979, 11, N.2, pp.33-38) comprising a source of modulated coherent radiation including a laser and a modulator and optically connected with a movable information carrier made as a sealed optical disk, a recording medium being coated on the internal surfaces of transparent walls of the disk, and an information addressing unit.
However this optical memory is deficient in that it is not very reliable and its recording density is not sufficiently high. It is not reliable because the optical disk is rather fragile and, also, because the working surfaces of the optical disk tend to deform by changes in the atmospheric pressure. Low recording density is due to variations in recording density for storage tracks having different radii. The resolution of the "dry" objective lens in the movable optical head is low which adds to this disadvantage, the numerical aperture of the lens cannot be larger than one.
The closest prior art, both technically and by the result obtained, is an optical memory (GB, A, No. 1 580 398) comprising optically connected elements: a source of modulated coherent radiation and a cylindrical information carrier equipped with a rotational drive. The cylindrical information carrier is a rigid nontransparent cylinder whose external surface is covered by a recording coating and which carries, by means of separating rings, an external relatively thin protective transparent cylinder. In the process of operation the external protective transparent cylinder rotates with the rigid nontransparent cylinder. The internal space of the cylindrical information carrier is communicated with the atmosphere in order to avoid deformation of the external protective cylinder by changes in the atmospheric pressure.
But this optical memory also has several disadvantages. Its recording density is low and it is not sufficiently reliable. Low recording density is due to the fact that the recording coating used to register information can be applied only on the external surface of the rigid nontransparent cylinder and, also, due to the use of a "dry" objective lens having a low numerical aperture. This optical memory is not reliable because the internal space of the cylindrical information carrier is not sealed off from the environment and, when the temperature conditions of the carrier change in the process of operation in relation to the temperature of the environment, this carrier "breathes" in or out. The internal space sucks in large amounts of dust, moisture, and other foreign bodies which are deposited on the surface of the recording coating, which substantially reduces reliability of information reading-recording. The reliability of this prior art memory device is also affected because the surface of the protective cylinder is often damaged in the process of its fast rotation.
This invention is to provide an optical storage device having such an arrangement as to increase the sharpness of focus of the radiation beam carrying information and, simultaneously, to make more dense recording more reliable.
This is achieved by that in an optical storage device comprising a source of modulated coherent radiation, which is optically connected to a cylindrical information carrier equipped with a drive for rotation, and provided with a recording coating applied on the substrate of the cylindrical information carrier, according to the invention, the cylindrical information carrier is disposed in a stationary cylindrical container having, in the side wall thereof, a window wherein a lens is placed to transmit modulated coherent radiation, said cylindrical container being filled with a liquid or gaseous medium for the radiation flux from the source of modulated coherent radiation and the length of said cylindrical container being at least twice as large as that of the recording coating applied on the substrate of the cylindrical information carrier equipped with a drive for axial motion.
Since the proposed optical memory makes use of a stationary lens, it permits much better adjustment of the optical system, the sharpness of focusing the flux of modulated coherent radiation on the surface of the recording coating of the cylindrical information carrier can be drastically improved. Since the cylindrical information carrier is arranged inside a stationary cylindrical container, it is well protected from damage and dirt, thus making information storage more reliable. The lens is placed in a window in the wall of the stationary cylindrical container and, during addressing, the cylindrical carrier has to be axially moved in relation to the stationary container. The length of the inner space of the cylindrical container should, therefore, be equal to or exceed the double length of the recording coating on the cylindrical information carrier.
Advisably, when the cylindrical container is being filled with a gaseous medium, the axial drive of the cylindrical information carrier should be the electric linear drive whose stationary part is disposed on the lateral wall of the cylindrical container, while the movable part thereof is placed on at least one butt face of the cylindrical movable information carrier.
It is also advisable that, when the cylindrical container is being filled with a liquid medium, the drive for axial motion of the cylindrical information carrier should be a reversible hydraulic drive whose piston is the cylindrical information carrier and whose cylinder is the cylindrical container, while the working fluid is the liquid medium which is desirably a low-viscosity immersion oil.
It is desirable that at least one impermeable radial partition should be placed in the internal space of the cylindrical information carrier.
It is also advisable that a protective coating should be applied on the recording coating provided on the base of the cylindrical information carrier.
Since the cylindrical information carrier of the proposed optical memory is disposed within a cylindrical container filled with immersion oil, the numerical aperture of the objective lens can be significantly increased and the sharpness of focusing of the radiation flux can, therefore, be substantially improved. The axial hydraulic drive becomes extremely convenient for addressing information. The cylindrical information carrier is provided with impermeable radial partitions in order to increase its hydraulic resistance and improve the efficiency of the hydraulic drive. The purpose of the protective coating is to prolong the service life of the recording coating on the cylindrical information carrier in the working fluid medium.